New Insights on the LAB-Staphylococcus aureus Interaction: A Transcriptomic Approach

The impact of lactic acid bacteria (LAB) on Staphylococcus aureus growth and enterotoxin production is the focus of several studies targeting food safety. LAB-mediated inhibition in foods often involves rapid pH decrease, nutrient competition and the production of several antagonistic substances, including bacteriocins. The challenges in studying bacterial interactions in complex food systems, such as raw milk and cheese, can be overcome by using Next Generation Sequencing based methodologies, once these techniques can provide a broader perspective on this specific issue. Therefore, we considered a RNA sequencing approach to study the occurrence of interactions between an enterotoxigenic S. aureus (ATCC 29213) and a bacteriocin-producing Enterococcus faecalis strain, previously isolated from raw milk cheese. These strains were inoculated alone or in combination in skim milk and the kinetics of bacterial growth, bacteriocin and enterotoxin production were monitored for 48 h at 30°C. Phenotypic analysis revealed a lack of enterotoxin production in mixed culture with minor impact on S. aureus final population. Preliminary metatranscriptomic analysis revealed a negative impact of E. faecalis on the expression of global regulators of S. aureus virulence, such as agr and sar. Also, the expression of oxidative and acidic stress related genes in S. aureus was altered. Considering these data, transcriptomic-based techniques constitute reliable tools for the study of bacterial behavior in food systems and may eventually help us to develop new ways of approaching food safety.